Mybatis的Environment解析详解

今天来具体看一下如何解析environments
//XMLConfigBuilder

Java代码

private void parseConfiguration(XNode root)
{
try
{
propertiesElement(root.evalNode("properties"));
typeAliasesElement(root.evalNode("typeAliases"));
pluginElement(root.evalNode("plugins"));
objectFactoryElement(root.evalNode("objectFactory"));
objectWrapperFactoryElement(root.evalNode("objectWrapperFactory"));
settingsElement(root.evalNode("settings"));
//解析environments
environmentsElement(root.evalNode("environments"));
databaseIdProviderElement(root.evalNode("databaseIdProvider"));
typeHandlerElement(root.evalNode("typeHandlers"));
mapperElement(root.evalNode("mappers"));
}
catch(Exception e)
{
throw new BuilderException((new StringBuilder()).append("Error parsing SQL Mapper Configuration. Cause: ").append(e).toString(), e);
}
}
//解析environments
private void environmentsElement(XNode context)
throws Exception
{
if(context != null)
{
if(C == null)
environment = context.getStringAttribute("default");
Iterator i$ = context.getChildren().iterator();
//遍历environments的child节点environment，并解析
do
{
if(!i$.hasNext())
break;
XNode child = (XNode)i$.next();
String id = child.getStringAttribute("id");
//如果environment的id属性，与environments的default相同时，才解析
if(isSpecifiedEnvironment(id))
{
//解析transactionManager
TransactionFactory txFactory = transactionManagerElement(child.evalNode("transactionManager"));
//解析dataSource
DataSourceFactory dsFactory = dataSourceElement(child.evalNode("dataSource"));
javax.sql.DataSource dataSource = dsFactory.getDataSource();
org.apache.ibatis.mapping.Environment.Builder environmentBuilder = (new org.apache.ibatis.mapping.Environment.Builder(id)).transactionFactory(txFactory).dataSource(dataSource);
configuration.setEnvironment(environmentBuilder.build());
}
} while(true);
}
}

//解析transactionManager
先看configuration的构造，启动有JDBC，POOLED类型的映射关系，这个在解析environment节点时，需要用到下载

Java代码

typeAliasRegistry.registerAlias("JDBC", org/apache/ibatis/transaction/jdbc/JdbcTransactionFactory);
typeAliasRegistry.registerAlias("POOLED", org/apache/ibatis/datasource/pooled/PooledDataSourceFactory);

Java代码

public Configuration()
{
safeRowBoundsEnabled = false;
safeResultHandlerEnabled = true;
mapUnderscoreToCamelCase = false;
aggressiveLazyLoading = true;
multipleResultSetsEnabled = true;
useGeneratedKeys = false;//允许JDBC支持生成的键
useColumnLabel = true;
cacheEnabled = true;//全局的映射器启用或禁用缓存
callSettersOnNulls = false;
localCacheScope = LocalCacheScope.SESSION;//本地一级缓存作用域
jdbcTypeForNull = JdbcType.OTHER;
lazyLoadTriggerMethods = new HashSet(Arrays.asList(new String[] {
"equals", "clone", "hashCode", "toString"
}));
defaultExecutorType = ExecutorType.SIMPLE;
autoMappingBehavior = AutoMappingBehavior.PARTIAL;
variables = new Properties();
objectFactory = new DefaultObjectFactory();//默认ObjectFactory
objectWrapperFactory = new DefaultObjectWrapperFactory();//默认DefaultObjectWrapperFactory
mapperRegistry = new MapperRegistry(this);
lazyLoadingEnabled = false;
interceptorChain = new InterceptorChain();//插件链
typeHandlerRegistry = new TypeHandlerRegistry();//类型处理注册器
typeAliasRegistry = new TypeAliasRegistry();//类型别名注册器
languageRegistry = new LanguageDriverRegistry();
//mappedStatements Map
mappedStatements = new StrictMap("Mapped Statements collection");
//mappedStatements，method，二级缓存
caches = new StrictMap("Caches collection");
//MapperInterface 方法返回结果类型Map
resultMaps = new StrictMap("Result Maps collection");
//MapperInterface 方法参数类型Map
parameterMaps = new StrictMap("Parameter Maps collection");
//主键生成器Map
keyGenerators = new StrictMap("Key Generators collection");
loadedResources = new HashSet();
//Mapper.xml 中statement片段
sqlFragments = new StrictMap("XML fragments parsed from previous mappers");
//未解析处理的statements
incompleteStatements = new LinkedList();
//未解析处理的CacheRefs
incompleteCacheRefs = new LinkedList();
//未解析处理的ResultMaps
incompleteResultMaps = new LinkedList();
//未解析处理的Methods
incompleteMethods = new LinkedList();
cacheRefMap = new HashMap();
typeAliasRegistry.registerAlias("JDBC", org/apache/ibatis/transaction/jdbc/JdbcTransactionFactory);
typeAliasRegistry.registerAlias("MANAGED", org/apache/ibatis/transaction/managed/ManagedTransactionFactory);
typeAliasRegistry.registerAlias("JNDI", org/apache/ibatis/datasource/jndi/JndiDataSourceFactory);
typeAliasRegistry.registerAlias("POOLED", org/apache/ibatis/datasource/pooled/PooledDataSourceFactory);
typeAliasRegistry.registerAlias("UNPOOLED", org/apache/ibatis/datasource/unpooled/UnpooledDataSourceFactory);
typeAliasRegistry.registerAlias("PERPETUAL", org/apache/ibatis/cache/impl/PerpetualCache);
typeAliasRegistry.registerAlias("FIFO", org/apache/ibatis/cache/decorators/FifoCache);
typeAliasRegistry.registerAlias("LRU", org/apache/ibatis/cache/decorators/LruCache);
typeAliasRegistry.registerAlias("SOFT", org/apache/ibatis/cache/decorators/SoftCache);
typeAliasRegistry.registerAlias("WEAK", org/apache/ibatis/cache/decorators/WeakCache);
typeAliasRegistry.registerAlias("VENDOR", org/apache/ibatis/mapping/VendorDatabaseIdProvider);
typeAliasRegistry.registerAlias("XML", org/apache/ibatis/scripting/xmltags/XMLLanguageDriver);
typeAliasRegistry.registerAlias("RAW", org/apache/ibatis/scripting/defaults/RawLanguageDriver);
typeAliasRegistry.registerAlias("SLF4J", org/apache/ibatis/logging/slf4j/Slf4jImpl);
typeAliasRegistry.registerAlias("COMMONS_LOGGING", org/apache/ibatis/logging/commons/JakartaCommonsLoggingImpl);
typeAliasRegistry.registerAlias("LOG4J", org/apache/ibatis/logging/log4j/Log4jImpl);
typeAliasRegistry.registerAlias("JDK_LOGGING", org/apache/ibatis/logging/jdk14/Jdk14LoggingImpl);
typeAliasRegistry.registerAlias("STDOUT_LOGGING", org/apache/ibatis/logging/stdout/StdOutImpl);
typeAliasRegistry.registerAlias("NO_LOGGING", org/apache/ibatis/logging/nologging/NoLoggingImpl);
typeAliasRegistry.registerAlias("CGLIB", org/apache/ibatis/executor/loader/CglibProxyFactory);
typeAliasRegistry.registerAlias("JAVASSIST", org/apache/ibatis/executor/loader/JavassistProxyFactory);
languageRegistry.setDefaultDriverClass(org/apache/ibatis/scripting/xmltags/XMLLanguageDriver);
languageRegistry.register(org/apache/ibatis/scripting/defaults/RawLanguageDriver);
}

从上可以看出JDBC，POOLED类型别名的映射关系如下：
JDBC，JdbcTransactionFactory 下载
POOLED，PooledDataSourceFactory

Java代码

<environments default="development">
<environment id="development">
<transactionManager type="JDBC" />
<dataSource type="POOLED">
<property name="driver" value="${driver}" />
<property name="url" value="${url}" />
<property name="username" value="${username}" />
<property name="password" value="${password}" />
</dataSource>
</environment>
</environments>

Java代码

private TransactionFactory transactionManagerElement(XNode context)
throws Exception
{
if(context != null)
{
String type = context.getStringAttribute("type");
Properties props = context.getChildrenAsProperties();
//从类型解决器中，获取type对应的类型的实例，从上面的配置来看
//实际为JdbcTransactionFactory
TransactionFactory factory = (TransactionFactory)resolveClass(type).newInstance();
//设置JdbcTransactionFactory属性
factory.setProperties(props);
return factory;
} else
{
throw new BuilderException("Environment declaration requires a TransactionFactory.");
}
}

//JdbcTransactionFactory

Java代码

下载

public class JdbcTransactionFactory
implements TransactionFactory
{
public void setProperties(Properties properties)
{
}
//根据数据连接新建事务
public Transaction newTransaction(Connection conn)
{
return new JdbcTransaction(conn);
}
//根据数据源和事务级别和是否自动提交，新建事务
public Transaction newTransaction(DataSource ds, TransactionIsolationLevel level, boolean autoCommit)
{
return new JdbcTransaction(ds, level, autoCommit);
}
}

//TransactionFactory

Java代码

public interface TransactionFactory
{
public abstract void setProperties(Properties properties);
public abstract Transaction newTransaction(Connection connection);
public abstract Transaction newTransaction(DataSource datasource, TransactionIsolationLevel transactionisolationlevel, boolean flag);
}

现在来看一下jdbc事务

Java代码

下载

public class JdbcTransaction
implements Transaction
{
private static final Log log = LogFactory.getLog(org/apache/ibatis/transaction/jdbc/JdbcTransaction);
protected Connection connection;//数据库连接
protected DataSource dataSource;//数据源
protected TransactionIsolationLevel level;//事务级别
protected boolean autoCommmit;//自动提交属性
public JdbcTransaction(DataSource ds, TransactionIsolationLevel desiredLevel, boolean desiredAutoCommit)
{
dataSource = ds;
level = desiredLevel;
autoCommmit = desiredAutoCommit;
}
public JdbcTransaction(Connection connection)
{
this.connection = connection;
}
public Connection getConnection()
throws SQLException
{
if(connection == null)
openConnection();
return connection;
}
public void commit()
throws SQLException
{
if(connection != null && !connection.getAutoCommit())
{
if(log.isDebugEnabled())
log.debug((new StringBuilder()).append("Committing JDBC Connection [").append(connection).append("]").toString());
connection.commit();
}
}
public void rollback()
throws SQLException
{
if(connection != null && !connection.getAutoCommit())
{
if(log.isDebugEnabled())
log.debug((new StringBuilder()).append("Rolling back JDBC Connection [").append(connection).append("]").toString());
connection.rollback();
}
}
public void close()
throws SQLException
{
if(connection != null)
{
resetAutoCommit();
if(log.isDebugEnabled())
log.debug((new StringBuilder()).append("Closing JDBC Connection [").append(connection).append("]").toString());
connection.close();
}
}
protected void setDesiredAutoCommit(boolean desiredAutoCommit)
{
try
{
if(connection.getAutoCommit() != desiredAutoCommit)
{
if(log.isDebugEnabled())
log.debug((new StringBuilder()).append("Setting autocommit to ").append(desiredAutoCommit).append(" on JDBC Connection [").append(connection).append("]").toString());
connection.setAutoCommit(desiredAutoCommit);
}
}
catch(SQLException e)
{
throw new TransactionException((new StringBuilder()).append("Error configuring AutoCommit. Your driver may not support getAutoCommit() or setAutoCommit(). Requested setting: ").append(desiredAutoCommit).append(". Cause: ").append(e).toString(), e);
}
}
protected void resetAutoCommit()
{
try
{
if(!connection.getAutoCommit())
{
if(log.isDebugEnabled())
log.debug((new StringBuilder()).append("Resetting autocommit to true on JDBC Connection [").append(connection).append("]").toString());
connection.setAutoCommit(true);
}
}
catch(SQLException e)
{
log.debug((new StringBuilder()).append("Error resetting autocommit to true before closing the connection. Cause: ").append(e).toString());
}
}
//获取connection
protected void openConnection()
throws SQLException
{
if(log.isDebugEnabled())
log.debug("Openning JDBC Connection");
connection = dataSource.getConnection();
if(level != null)
connection.setTransactionIsolation(level.getLevel());
setDesiredAutoCommit(autoCommmit);
}
}

//Transaction

Java代码

public interface Transaction
{
public abstract Connection getConnection()
throws SQLException;
public abstract void commit()
throws SQLException;
public abstract void rollback()
throws SQLException;
public abstract void close()
throws SQLException;
}

从上面可以看出jdbc对应的事务工厂为JdbcTransactionFactory，由JdbcTransactionFactory，根据数据源，事务级别以及自动提交属性来，创建JdbcTransaction，而JdbcTransaction的事务管理，是通过数据连接connection，而connection是从datasource获取，JdbcTransaction的事务管理，就是依靠相应的数据库driver，来管理，实际依赖于数据库。下载

//解析dataSource

Java代码

private DataSourceFactory dataSourceElement(XNode context)
throws Exception
{
if(context != null)
{
//获取数据源的类型，和属性
String type = context.getStringAttribute("type");
Properties props = context.getChildrenAsProperties();
//根据type从configuration的类型处理器，获取具体的DataSourceFactory
//从上文，我们看一看到type为POOLED，对应的是PooledDataSourceFactory
DataSourceFactory factory = (DataSourceFactory)resolveClass(type).newInstance();
factory.setProperties(props);
return factory;
} else
{
throw new BuilderException("Environment declaration requires a DataSourceFactory.");
}
}

// PooledDataSourceFactory

Java代码

public class PooledDataSourceFactory extends UnpooledDataSourceFactory
{
public PooledDataSourceFactory()
{
dataSource = new PooledDataSource();
}
}

来源：oschina

链接：https://my.oschina.net/u/2992866/blog/778142

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